Embracing variability: environmental dependence and plant community context in ecological restoration

In heterogeneous landscapes, one can expect a complexity of ecological restoration outcomes. The effectiveness of management often depends on environmental conditions (environmental context) and how management indirectly affects other components of the system (community context). Although managers appreciate this context dependency, it is difficult to translate it to decision-making in restoration. We demonstrate one approach to improve this translation. We surveyed plant, soil, and landscape characteristics at 131 grassland and coastal sage sites that received herbicide treatments to remove non-native plant species and/or propagule addition to increase native species. We used path analysis to describe how each management approach influenced target non-native species and how interactions with environmental conditions and indirect effects of management influenced plant community composition. This approach enabled us to analyze a complex system with differing management histories to identify both direct and indirect effects of management. Management had the intended direct effects: the application of herbicide and propagule addition directly reduced non-native species and increased native species, respectively. We found little evidence of environmental dependency: effects occurred largely independent of environmental conditions. However, management outcomes did depend on plant community context. Specifically, although herbicide reduced the cover of target, non-native plant species, this reduction resulted in only slight increases in native species and instead led indirectly to increases in non-targeted, non-native species. We suggest that quantitative evaluation of variability in restoration outcomes allows management to be more adaptive and increase decision-making efficacy in complex managed landscapes.